Formed glass sheets are used extensively for vehicle windshields, side windows, and rear windows. To improve the mechanical strength of the glass, the formed glass sheets are also conventionally tempered which causes the glass to break into relatively small, dull pieces rather than into relatively long, sharp shards. In the United States, tempered formed glass sheets are used on vehicle side and rear windows while annealed formed glass sheets laminated to each other by polyvinyl butyral are used for vehicle windshields. In other countries, tempered formed glass sheets are used for vehicle windshields as well as side and rear windows.
One prior art glass sheet forming system disclosed by U.S. Pat. No. 3,782,816 Powell et al includes a heating conveyor on which a glass sheet is heated prior to conveyance to a bending station where the heated glass sheet is received by rollers of an upwardly facing convex mold surface on a rotatable mold carrying member. Downward retraction of the rollers into the mold surface and subsequent pressing of the heated flat glass sheet between the upwardly facing surface and a downwardly facing surface on an upper mold forms the glass sheet prior to rotation of the mold carrying member and release of the formed glass sheet chilling by an oil bath that toughens or tempers the glass sheet.
Another prior art forming system disclosed by U.S. Pat. No. 3,778,244 Nedelec et al includes a heating conveyor that conveys a flat glass sheet during heating and delivers the heated glass sheet to a bending station which includes a vertically movable upper mold having a downwardly facing surface of a curved shape against which the heated glass sheet is received from the heating conveyor for pneumatic forming. Upward movement of the upper mold then permits a lower mold with a curved surface to move below the upper mold. In one embodiment, the upper mold has a downwardly concave shape and the lower mold has an upwardly convex shape that receives the previously formed glass sheet from the upper mold and thereafter transfers the formed glass sheet from below the upper mold to a cooling and conditioning chamber. In another embodiment, the upper mold has a downwardly convex shape and the lower mold has an upwardly concave shape for receiving the heated glass sheet from the upper mold.
U.S. Pat. Nos. 4,204,854 McMaster et al; 4,282,026 McMaster et al; 4,233,049 Seymour; 4,575,390 McMaster; and 4,609,391 McMaster disclose glass sheet forming systems wherein a holder has a downwardly facing surface that receives a heated glass sheet from a heating conveyor and then transfers the heated glass sheet to a lower mold of an upwardly concave shape for forming under gravity.
The above mentioned prior art references and U.S. Pat. Nos. 4,661,141 Nitschke et al; 4,711,653 Frank et al; 4,746,348 Frank et al; and 4,859,225 Kuster et al disclose pressing and vacuum forming of glass sheets between upper and lower molds.
U.S. Pat. Nos. 4,578,103 and 4,615,724 of Fackelman each disclose a glass sheet forming system which includes a topside transfer apparatus including a fused silica block having a downwardly facing flat surface at which a vacuum is drawn through a first set of holes and at which pressurized gas is supplied through a second set of holes in order to support a heated glass sheet without any direct contact. The topside transfer apparatus receives a heated glass sheet from a heating conveyor and subsequently releases the heated glass sheet onto a lower mold which is specifically disclosed as having an upwardly concave shape. Another experimental glass sheet topside support device is disclosed by U.S. Pat. No. 3,223,443 Misson and includes inverted cup-shaped members that are spaced from each other to provide both pressurized gas and a vacuum that cooperatively support a glass sheet without any engagement.